Heretofore, an exhaust gas recirculation (EGR) is performed in a diesel engine, for example. Specifically, exhaust gas is partially recirculated into intake pipe in order to reduce nitrogen oxides (NOx) contained in exhaust gas. However, exhaust gas contains unburned fuel, engine oil, soot, and the like, in addition to gaseous substances such as the NOx. When these components are deposited and solidified on the inwall surface of an EGR passage, an operation of an EGR valve may be disturbed.
For example, according to JP-A-2003-314377, an EGR valve is actuated when a diesel engine stops, thereby removing foreign matters deposited on the inwall surface of the EGR passage.
However, in this disclosure, the EGR valve is actuated for a predetermined number and at a predetermined intensity, irrespective of an extent of the deposition of foreign matters such as a deposition quantity and a deposition intensity. Accordingly, it is difficult to efficiently remove foreign matters. Specifically, when the deposition quantity of foreign matters is small or when the deposition intensity thereof is low, the number of the actuations of the EGR valve and the intensity of the actuations are unnecessarily afforded, and hence, a wasteful energy consumption increases. To the contrary, when the deposition quantity of foreign matters is large or when the deposition intensity thereof is high, the number of the actuations of the EGR valve and the intensity of the actuations become insufficient, and hence, foreign matters are left behind without being sufficiently removed.